Messages in this thread | | | Subject | Re: [PATCH 2/7] nohz: New tick dependency mask | From | Chris Metcalf <> | Date | Tue, 24 Nov 2015 11:19:15 -0500 |
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On 11/13/2015 09:22 AM, Frederic Weisbecker wrote: > The tick dependency is evaluated on every IRQ. This is a batch of checks > which determine whether it is safe to stop the tick or not. These checks > are often split in many details: posix cpu timers, scheduler, sched clock, > perf events. Each of which are made of smaller details: posix cpu > timer involves checking process wide timers then thread wide timers. Perf > involves checking freq events then more per cpu details. > > Checking these details asynchronously every time we update the full > dynticks state bring avoidable overhead and a messy layout. > > Lets introduce instead tick dependency masks: one for system wide > dependency (unstable sched clock), one for CPU wide dependency (sched, > perf), and task/signal level dependencies. The subsystems are responsible > of setting and clearing their dependency through a set of APIs that will > take care of concurrent dependency mask modifications and kick targets > to restart the relevant CPU tick whenever needed. > > This new dependency engine stays beside the old one until all subsystems > having a tick dependency are converted to it. > > > +void tick_nohz_set_dep_cpu(enum tick_dependency_bit bit, int cpu) > +{ > + unsigned long prev; > + struct tick_sched *ts; > + > + ts = per_cpu_ptr(&tick_cpu_sched, cpu); > + > + prev = fetch_or(&ts->tick_dependency, BIT_MASK(bit)); > + if (!prev) { > + preempt_disable(); > + /* Perf needs local kick that is NMI safe */ > + if (cpu == smp_processor_id()) { > + tick_nohz_full_kick(); > + } else { > + /* Remote irq work not NMI-safe */ > + WARN_ON_ONCE(in_nmi());
Better to say "if (!WARN_ON_ONCE(in_nmi()))" here instead so we don't actually try to kick if we are in an NMI?
-- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com
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